An active stylus is an electronic product that transmits a signal by using a stylus tip, while a screen side receives the signal and demodulates the signal to obtain stylus tip position information and other information. In addition to a stylus tip position function, an existing active stylus generally has other functions such as a pressure detection function and a key function etc. For stylus tip positioning, an active stylus only needs to transmit a signal having a fixed frequency. A screen side receives the signal by using sensing channels that are arranged in a certain shape, and determines the position of a stylus tip on the screen according to signal strengths detected by the sensing channels. As a pressure sensor, a button or another sensor is all disposed on an active stylus, pressure information, button information or other information on the active stylus is necessary to be transmitted through a stylus tip to a screen in a particular way, and the screen demodulates to obtain the information.
Currently, there are two main methods for transmitting pressure information, button information or other information by commercially available active stylus products. In one method, a binary coding is used. As shown in FIG. 1, a binary code is used in encoding. A frequency-modulated signal of a coordinate position is combined with a pressure signal or a function key pressing signal to form an encoded signal. Each bit of the encoding is amplitude modulated. Information is transmitted by combination coding of 1 and 0. Each bit is determined according to the demodulated amplitude of a signal. When the amplitude exceeds a threshold value, a bit is determined as 1. When the amplitude is less than the threshold value, a bit is determined as 0. In another method, frequency modulation is used. As shown in FIG. 2, a frequency-modulated signal of a coordinate position is combined with a stylus tip pressure signal or a function key pressing signal to form an encoded signal. Information of the encoded signal is frequency modulated, where each frequency represents certain information. The certain information is modulated by using a corresponding frequency. Frequency demodulation is performed by a screen side to obtain the information.
However, during the implementation of the present disclosure, the inventor(s) finds that the existing techniques at least have the following issues: A main disadvantage of the binary coding method is that each coding bit only has two states 0 and 1, which contains a relatively small amount of information. To transmit more information, it is necessary to increase the amount of coding bits. In this case, information encoding takes a long time, and a refresh rate may be reduced. In the method of frequency modulation, to transmit more information, a bandwidth of a frequency-modulated signal may be increased, so that a larger bandwidth is available for information encoding. Alternatively, a frequency may be modulated in a more refined manner so that frequency resolution can be increased to obtain more information while a bandwidth remains unchanged. In such a case, there are higher requirements on the hardware performance for frequency modulation and demodulation. Moreover, demodulation resolution is directly proportional to the time duration of a signal. A demodulator requires a longer signal time duration to obtain better frequency resolution.
Therefore, it becomes more important to improve the efficiency of information transmission between an active stylus and a screen side.